Method for transmitting radio signals, radio communication access network and terminal using same

ABSTRACT

The invention concerns a method wherein a radio link control stage processes separately first data units containing information items of a specific type and second data units not containing information items of said type. A control stage for access to the media delivers the first data units through a first dedicated transport channel and the second data units through a second dedicated transport channel. The data units delivered through said dedicated transport channels are supplied to an encoding and multiplexing stage to form at least a train of symbols relative to a dedicated physical channel and supplied to a radio transmission stage. The encoding and multiplexing stage and/or the radio transmission stage ensure greater protection against noise through the first dedicated transport channel than through the second dedicated transport channel.

BACKGROUND OF THE INVENTION

The present invention relates to the field of radio communications, andin particular to the techniques making it possible to form various typesof dedicated channels for transmitting radio signals destined for agiven station.

The invention finds application in particular in third-generationcellular networks of the UMTS type (“Universal Mobile TelecommunicationSystem”) using code-division multiple access (CDMA) techniques.

The fact that the dedicated signaling information and the traffic (voiceor data) are transmitted over the radio interface with the same degreeof immunity to noise is a limitation of certain radio communicationsystems. The radio coverage must be at least as great for the signalingas for the traffic. Otherwise, undesirable situations may occur, such asthe inability of a subscriber to put an end to a communication inprogress, or the inability to execute a cell transfer (“handover”), etc.

Furthermore, in certain cases, such as for example when an adaptivemulti-rate (AMR) codec is used to code speech, the immunity to noise maybe enhanced by increasing the redundancy introduced by the channelcoding and by correspondingly reducing the instantaneous bit rate of thesource coder. In such cases, it is also desirable to be able to increasethe noise immunity of the dedicated signaling.

U.S. Pat. No. 5,230,082 tackles the above problem, as regards the riskof inability to execute a handover when it is no longer possible for amobile terminal to pick up the signaling information controlling suchhandover. The document proposes a mechanism through which a base stationneighboring the one which was previously serving the mobile terminalborrows the physical communication resource to deliver the handovercommand to the terminal. This mechanism lacks flexibility and requirescooperation between the base stations as well as a dynamic scheme forradio resource allocation in the network infrastructure.

Moreover, a user data flow can contain control information mixed withthe traffic, in particular control information from the higher layers ofthe OSI model (network, transport or application). Here again, it may besensible to protect the control or signaling information more than thetraffic data, which is not allowed by the current systems.

An object of the present invention is to propose a method meeting theabove requirements.

SUMMARY OF THE INVENTION

The invention thus proposes a method of transmitting radio signals basedon at least one data flow toward a radio communication station,comprising the steps of:

processing separately, in a radio link control stage first data unitscontaining information of a specified type and second data units notcontaining information of the specified type;

supplying the data units to a medium access control stage which deliversthe first data units along a first dedicated transport channel and thesecond data units along at least one second dedicated transport channel;

supplying the data units delivered along said dedicated transportchannels to a coding and multiplexing stage to form at least one symbolstream pertaining to a dedicated physical channel; and

supplying each symbol stream to a radio transmission stage,

and wherein the coding and multiplexing stage and/or the radiotransmission stage are controlled to provide greater protection againstnoise along the first dedicated transport channel than along the seconddedicated transport channel.

The information of said specified type is preferably informationpertaining to a signaling protocol, whereas the “second data units”rather contain user data.

Several processes may be used to differentiate between the anti-noiseprotections afforded to the various transport channels. The coding andmultiplexing stage can thus be controlled to apply a channel codingexhibiting a higher redundancy in the first dedicated transport channelthan in the second dedicated transport channel.

In an advantageous embodiment, the coding and multiplexing stage iscontrolled to form a first symbol stream relating to a first dedicatedphysical channel based on the first dedicated transport channel, and atleast one second symbol stream relating to a second dedicated physicalchannel based on at least one second dedicated transport channel.

Thus, the radio transmission stage can be so controlled that the radiosignals transmitted have a first component along the first dedicatedphysical channel and a second component along the second dedicatedphysical channel, and that the first component has a greatertransmission power than the second component. Another possibility, whenthe dedicated physical channels are multiplexed by a spread spectrumtechnique, is to control the coding and multiplexing stage and the radiotransmission stage so that the first symbol stream has a smaller symbolbit rate than the second symbol stream, and that the first dedicatedphysical channel is associated with a higher spreading factor than thesecond dedicated physical channel.

Yet another possibility is to take advantage of the multiple receiversprovided in certain radio communication terminals, especially whenoperated in macrodiversity mode, i.e. when the terminal communicatessimultaneously with a plurality of base stations (see WO 00/38642). Inthe latter case, the radio signals can be transmitted from at least twobase stations, the radio transmission stage being apportioned among saidbase stations, while arranging for the first and second symbol streamsto be supplied to the radio transmission stage in distinct basestations, so as to form radio signals transmitted along differentpropagation paths.

In one embodiment of the method, the radio link control stage separatelyreceives a first data flow belonging to a control plane, from which itforms the first data units, and at least one second data flow belongingto a user plane, from which it forms some at least of the second dataunits. The information of the specified type may then comprise radioresources control information and/or mobility management informationand/or call control information.

In another embodiment, the radio link control stage receives a data flowbelonging to a user plane, from which it forms the data units, whilediscriminating the first and second data units based on an analysis ofsaid flow.

Other aspects of the present invention relate to an access network for aradio communication system and to a radio communication terminal, whichcomprise a radio link control stage, a medium access control stage, acoding and multiplexing stage and a radio transmission stage, which arearranged to implement a method of transmitting radio signals as definedhereinabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a UMTS network to which the invention may beapplied;

FIG. 2 is a chart showing the layer organization of communicationprotocols employed on the radio interface of the UMTS network;

FIG. 3 is a schematic diagram of a coding and multiplexing stage of abase station of the network;

FIG. 4 is a schematic diagram of a radio transmission stage of the basestation;

FIG. 5 is a chart illustrating a set of codes for separating channelsusable in a cell of the network;

FIG. 6 is a partial schematic diagram of an exemplary access networkaccording to the invention;

FIG. 7 is a partial schematic diagram of an exemplary radiocommunication terminal according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is described below in its application to a UMTS networkoperating in FDD (frequency division duplex) mode. FIG. 1 shows thearchitecture of such a UMTS network.

The mobile service switches 10, belonging to a core network (CN), arelinked on the one hand to one or more fixed networks 11 and on the otherhand, by means of a so-called lu interface, to control equipment 12 orRNCs (“Radio Network Controllers”). Each RNC 12 is linked to one or morebase stations 13 by means of a so-called lub interface. The basestations 13, distributed over the territory covered by the network, arecapable of communicating by radio with the mobile terminals 14, 14 a, 14b called UE (“UMTS Equipment”). The base stations can be groupedtogether to form nodes called “node B”. Certain RNCs 12 may furthercommunicate with one another by means of a so-called lur interface. TheRNCs and the base stations form an access network called UTRAN (“UMTSTerrestrial Radio Access Network”).

The UTRAN comprises elements of layers 1 and 2 of the OSI model forproviding the links-required on the radio interface (called Uu), and aradio resource control (RRC) stage 15A belonging to layer 3, asdescribed in the 3G TS 25.301 technical specification “Radio InterfaceProtocol” version 3.2.0 published in October 1999 by the 3GPP (3^(rd)Generation Partnership Project). Seen from the higher layers, the UTRANacts simply as a relay between the UE and the CN.

FIG. 2 shows the RRC stages 15A, 15B and the lower layer stages whichbelong to the UTRAN and to a UE. On each side, layer 2 is subdividedinto a radio link control (RLC) stage 16A, 16B and a medium accesscontrol (MAC) stage 17A, 17B. Layer 1 comprises a coding andmultiplexing stage 18A, 18B. A radio stage 19A, 19B caters for thetransmission of the radio signals from symbol streams provided by stage18A, 18B, and the reception of the signals in the other direction.

There are various ways of adapting the architecture of protocolsaccording to FIG. 2 to the hardware architecture of the UTRAN accordingto FIG. 1, and in general various organizations can be adopted dependingon the types of channels (see section 11.2 of the 3G TS 25.401 technicalspecification “UTRAN Overall Description”, version 3.1.0 published inJanuary 2000 by the 3GPP). The RRC, RLC and MAC-stages are located inthe RNC 12. When several RNCs are involved, the MAC sublayer can beapportioned among these RNCs, with appropriate protocols for theexchanges on the lur interface, for example ATM (“Asynchronous TransferMode”) and AAL2 (“ATM Adaptation Layer No. 2”). These same protocols mayalso be employed on the lub interface for the exchanges between the MACsublayer and layer 1. During exchanges in macrodiversity mode, an RNCcan include part of layer 1, involved in macrodiversity functions.

Layers 1 and 2 are each controlled by the RRC sublayer, whose featuresare described in the 3G TS 25.331 technical specification “RRC ProtocolSpecification”, version 3.1.0 published in October 1999 by the 3GPP. TheRRC stage 15A, 15B supervises the radio interface. Moreover, itprocesses flows to be transmitted to the remote station according to a“control plane”, as opposed to the “user plane” which corresponds to theprocessing of the user data arising from layer 3.

The RLC sublayer is described in the 3G TS 25.322 technicalspecification “RLC Protocol Specification”, version 3.1.2 published inOctober 1999 by the 3GPP. In the transmit direction, the RLC stage 16A,16B receives, according to the respective logical channels, data flowsconsisting of service data units (RLC-SDU) arising from layer 3. An RLCmodule of stage 16A, 16B is associated with each logical channel so asin particular to perform a segmentation of the RLC-SDU units of the flowinto protocol data units (RLC-PDU) addressed to the MAC sublayer andcomprising an optional RLC header. In the receive direction, an RLCmodule conversely performs a reassembling of the RLC-SDU units of thelogical channel from the data units received from the MAC sublayer.

The MAC sublayer is described in the 3G TS 25.321 technicalspecification “MAC Protocol Specification”, version 3.1.0 published inOctober 1999 by the 3GPP. It maps one or more logical channels onto oneor more transport channels (TrCH). In the transmit direction, the MACstage 17A, 17B can multiplex one or more logical channels into onetransport channel. On such a transport channel, the MAC stage 17A, 17Bdelivers successive transport blocks TrBk each consisting of an optionalMAC header and an RLC-PDU unit arising from an associated logicalchannel.

For each TrCH, the RRC sublayer provides the MAC sublayer with atransport format set (TFS). A transport format comprises a transmissiontime interval (TTI) equal to 10, 20, 40 or 80 ms, a transport blocksize, a transport block set size and parameters defining the protectionscheme to be applied in the TrCH by layer 1 for detecting and correctingtransmission errors. Depending on the current bit rate on the logicalchannel or channels associated with the TrCH, the MAC stage 17A, 17Bselects a transport format from the TFS assigned by the RRC sublayer,and it delivers in each TTI a set of transport blocks complying with theselected format, whilst indicating this format to layer 1.

Layer 1 can multiplex several TrCHs on a given physical channel. In thiscase, the RRC sublayer assigns a transport format combination set (TFCS)to the physical channel, and the MAC sublayer dynamically selects acombination of transport formats from this TFCS, thereby defining thetransport formats to be used in the various multiplexed TrCHs.

UMTS uses the spread spectrum CDMA technique, i.e. the transmittedsymbols are multiplied by spreading codes consisting of samples called“chips” whose rate (3.84 Mchip/s in the case of UMTS) is greater thanthat of the symbols transmitted. The spreading codes distinguish variousphysical channels PhCH which are superimposed on the same transmissionresource consisting of a carrier frequency. The auto- andcross-correlation properties of the spreading codes enable the receiverto separate the PhCHs and to extract the symbols intended therefor. ForUMTS in FDD mode on the downlink, a scrambling code is allocated to eachbase station, and various physical channels used by this base stationare distinguished by mutually orthogonal channel codes (“channelizationcodes”). The base station can also use several mutually orthogonalscrambling codes. On the uplink, the base station uses the scramblingcode to separate the transmitting UEs, and possibly the channel code toseparate the physical channels arising from one and the same UE. Foreach PhCH, the overall spreading code is the product of the channel codeand the scrambling code. The spreading factor (equal to the ratio of thechip rate to the symbol rate) is a power of 2 lying between 4 and 512.This factor is chosen as a function of the bit rate of symbols to betransmitted on the PhCH.

The various physical channels are organized in 10 ms frames which followone another on the carrier frequency used by the base station. Eachframe is subdivided into 15 time slots of 666 μs. Each slot can carrythe superimposed contributions of one or more physical channels,comprising common channels and dedicated physical channels (DPCH). Thecontribution from a DPCH to a time slot in FDD mode comprises:

a number of pilot symbols placed at the end of the slot. Known a priorito the recipient, these symbols allow the recipient to acquiresynchronization and to estimate parameters useful for demodulating thesignal;

a transport format combination indicator (TFCI), placed at the start ofthe slot; this TFCI arises from the MAC sublayer;

a transmit power control (TPC) information to be used by the recipienton the reverse link; this command arises from a layer 1 power controlmodule which uses servo-control parameters arising from the RRCsublayer;

two data fields, denoted DATA1 and DATA2, placed on either side of theTPC field.

The DPCH can thus be viewed as including a dedicated physical controlchannel, or DPCCH, corresponding to the TFCI, TPC and PL fields, and adedicated physical data channel, or DPDCH, corresponding to the DATA1and DATA2 fields.

For one and the same communication, it is possible to establish severalDPCHs corresponding to different channel codes, whose spreading factorsmay be equal or different. This situation is encountered in particularwhen a DPDCH is not sufficient to provide the transmission bit raterequired by the application. In what follows, Y denotes the number,equal to or greater than 1, of physical channels used for one and thesame communication in one direction.

Furthermore, this same communication can use one or more transportchannels. Multiplexed TrCHs are for example used for multimediatransmissions, in which signals of different kinds to be transmittedsimultaneously require different transport characteristics, especiallyas regards protection against transmission errors. Moreover, certaincoders may deliver, in order to represent a given signal (e.g. audio), aplurality of symbol flows having different perceptual importances andtherefore requiring different degrees of protection. Multiple TrCHs arethen used to transport these various symbol flows. In what follows, Xdenotes the number, equal to or greater than 1, of transport channelsused for a given communication on the aforesaid Y physical channels.

For each transport channel i (1≦i≦X), the TTI is composed of F_(i)consecutive frames, with F_(i)=1, 2, 4 or 8. Typically, the shorter thedelay with which the signal conveyed by the transport channel must bereceived, the shorter is the TTI used. For example, a TTI of 10 ms(F_(i)=1) will be used for a telephony application, while a TTI of 80 ms(F_(i)=8) may be used for a data transmission application.

The coding and the multiplexing of the X flows of information symbolsemanating from the TrCHs on the Y PhCHs are described in detail in the3G TS 25.212 technical specification “Multiplexing and channel coding(FDD)”, version 3.0.0 published in October 1999 by the 3GPP.

In the transmission direction, the stage 18A, 18B multiplexes the flowsa_(i) (1≦i≦X) relating to the X TrCHs used in a communication, to formwhat is called a coded composite transport channel, or CCTrCH, which issubsequently subdivided into one or more physical channels PhCH#j(1≦j≦Y) on which synchronized symbol flows, respectively denoted r_(j),are transmitted.

The coding and multiplexing stage 18A is described with reference toFIG. 3 in the direction of transmission from the UTRAN to a UE. Asimilar structure is provided for the uplink (see specification 3G TS25.212). The references bearing the index i designate the elementspertaining to TrCH i (1≦i≦X), the references bearing the index jdesignate the elements pertaining to PhCH j (1≦j≦Y), and the referenceswith no index pertain to the operations performed for each frame at theCCTrCH level.

The characteristics of the transport format are supplied to the codingblock 20 _(i) by the MAC stage 17A. The flow a_(i) to be transmitted oneach TRCH i is composed of successive TrBks. The module 21 _(i)completes each TrBk by adding thereto a cyclic redundancy checksum(CRC), serving to detect any transmission errors. The TrBk b_(i) arethen concatenated and/or segmented by the module 22 _(i) to form blockso_(i) of appropriate size for the input of the channel coder 23 _(i).

For each TTI of transport channel i, the channel coder 23 _(i) outputs asequence c_(i) of E_(i) coded bits denoted c_(i,m) (1≦m≦E_(i)). Twotypes of error correcting code may be applied by the module 23 _(i):

a convolutional code of rate ½ or ⅓ and of constraint length K=9;

a turbocode of rate ⅓ for the applications requiring the lowest errorrates.

The rate matching modules 24 _(i) delete (puncture) or repeat bits ofthe sequences c_(i) so as to match the bit rate of the TrCHs to theglobal bit rate allowable on the PhCH or PhCHs given their spreadingfactors.

The parameters of the CRC, of the channel coding and of the ratematching are defined in the transport format.

In a given frame, the periods devoted to the various TrCHs of thecommunication may have fixed positions (before the intra-frameinterleaving mentioned below) or variable positions. In the case offixed positions, it may be necessary to append to the sequence g_(i)delivered by the module 24 _(i), by means of the module 25 _(i), one ormore marked symbols, called DTX (“Discontinuous Transmission”) bits,which will not be transmitted.

The interleaving module 26 _(i) performs a permutation of the sequenceh_(i) delivered by the module 25 _(i), with a view to distributing thesymbols pertaining to the TTI over the F_(i) frames which it covers.This interleaving consists in writing the symbols of the sequence h_(i)successively to the rows of a matrix comprising F_(i) columns, inpermuting the columns of the matrix, and in then reading the symbols ofthe matrix column by column to form the sequence denoted q_(i). Themodule 27 _(i) then chops the sequence h_(i) into F_(i) segments ofconsecutive symbols corresponding to the F_(i) columns of theinterleaving matrix after permutation, and respectively assigns thesesegments to the F_(i) frames of the TTI to form a sequence denoted f_(i)for each frame and each TrCH i (1≦i≦X).

The sequences f_(i) produced for the various TrCHs of the communication(1≦i≦X) are multiplexed, i.e. placed one after the other, by a module 28forming a sequence s of S symbols for the CCTrCH. In the case where theperiods devoted to the various TrCHs of the communication have variablepositions, it may be necessary to append to the sequence s, by means ofthe module 29, one or more DTX bits.

Then, the module 30 chops the sequence w delivered by the module 29 intoY segments of U₁, U₂, . . . , U_(Y) consecutive symbols, andrespectively assigns these segments to the Y PhCHs to form a sequencedenoted u_(j) for each PhCH j (1≦j≦Y). The interleaving module 31 _(j)performs a permutation of the sequence u_(j), with a view todistributing the symbols, within the current frame, over the Y PhCHsemployed by the communication. This interleaving consists in writing thesymbols of the sequence u_(j) successively to the rows of a matrixcomprising thirty columns, in permuting the columns of the matrix, andin then reading the symbols of the matrix column by column to form thesequence, denoted v_(j), of U_(j) symbols.

The physical channel mapping module 32 _(j) finally distributes thesuccessive symbols of the sequence v_(j) into the fields DATA1 and DATA2of the time slots of the current frame. The module 32 _(j) furthercompletes the symbol stream r_(j) delivered by the stage 18A byinserting the appropriate signaling bits into the fields PL, TFCI andTPC of the DPCCH.

FIG. 4 illustrates the organization of the radio transmission stage 19A,19B of a base station 13 or of a UE 14, which multiplexes the PhCHs bythe CDMA technique. The information to be transmitted on a PhCH j formsthe subject of a first spreading by the channel code CC_(j).

The channel codes CC_(j) are orthogonal variable spreading factor (OVSF)codes. They are chosen from a set of codes of the same type as the treerepresented in FIG. 5. Each code c_(SF,i) (1≦i≦SF) is a sequence of SFchips, each taking the value ±1, with SF=2^(L−k), L being a positiveinteger (equal to 8 in the case of UMTS) and k an integer variable suchthat 0≦k≦L. The tree is defined by:

c _(1,1)=(1),

c _(2.SF,2i-1)=(c _(SF,i) ,c _(SF,i)),

c _(2.SF,2i)=(c _(SF,i) ,−c _(SF,i)),

The chips of a channel code c_(SF,i) modulate, at the rate D=3.84Mchip/s, symbol streams whose rate is D/SF=2^(k−L).D, i.e. the spreadingfactor equals SF=2^(L−k). The symbols in question are complex symbolseach comprising two signed bits (of value ±1) corresponding to an Ipathway and to a Q pathway.

The channel codes are allocated by the RRC sublayer. The codes allottedare chosen so as to be globally orthogonal for one transmitter. With thecode tree of FIG. 5, two codes having the same spreading factor arealways orthogonal, the sum of the chip-by-chip products being zero. Twocodes with spreading factors 2^(L−k) and 2^(L−k′) are orthogonal if,after they have modulated any two sequences of signed bits withrespective rates 2^(k−L).D and 2^(k′−L).D, the resulting chip sequencesare orthogonal. With the tree arrangement of FIG. 5, this amounts tosaying that two channel codes are orthogonal if and only if they do notbelong to one and the same branch of the tree, going from the rootc_(1,1) to a leaf c_(L,i). The selection of the codes by the RRCsublayer obeys this constraint globally: the set of channel codes CC_(j)used at the same instant by the transmitter is such that no two codesare found on the same branch. This allows the receivers to discriminatethe channels which concern them.

The RRC sublayer supplies, for each PhCH j formed by the coding andmultiplexing stage 18A, 18B, the spreading factor SF_(j) and the indexi_(j) of the channel code to be used. A generator 39 _(j) the stage 19A,19B delivers this code CC_(j)=C_(SFj,ij) to a multiplier 40 _(j) whichmodulates the complex symbols transmitted on the corresponding physicalchannel. The symbol sequences thus modulated are summed at 41 so as tocombine the multiple access channels.

Before the summator 41 (upstream or downstream of the multiplier 40_(j)), another multiplier 42 _(j) weights the contribution of each PhCHj by applying thereto a gain P(j) determined by a power control module43 _(j) as a function of commands TPC_(j) returned in the DPCCH on thereverse link. These commands TPC_(j) are obtained after estimation bythe receiver of the signal-to-interferer ratio (SIR) and comparison witha target value SIR_(target,j) given by the RRC sublayer, according to aservo-control procedure described in the 3G TS 25.214 technicalspecification “Physical layer procedures (FDD)”, version 3.1.1 publishedin December 1999 by the 3GPP.

The complex signal delivered by the summator 41 is multiplied at 44 bythe scrambling code SC supplied by a generator 45. The code SC isapplied identically to all the CDMA channels, except in the case of abase station using several scrambling codes.

At the output of the multiplier 44, the complex baseband signal isprocessed by a modulator 46 carrying out the pulse shaping and afour-state phase modulation (QPSK) to form the radio signal transmittedon the Uu interface.

The reception part of the stage 19A, 19B transposes the radio signalpicked up and amplified into baseband, then it multiplies it by thescrambling code and by the channel code CC_(j) of each PhCH to beprocessed. The estimated symbol streams thus recovered are submitted tothe stage 18A, 18B which undertakes the demultiplexing and decodingoperations which are the dual of the operations described with referenceto FIG. 3, thereby restoring the TrBks estimated in relation to thevarious TrCHs. When operating in macrodiversity mode, a combination ofthe TrBks estimated subsequent to reception along various routes isperformed to achieve the macrodiversity gain. The MAC stage 17A, 17Bnext undertakes the logical channel demultiplexing from the transportchannels, then the RLC stage 16A, 16B reassembles the data flowsintended for the higher layers.

FIG. 6 diagrammatically shows UTRAN entities involved in accordance withan embodiment of the invention in the sending of dedicated informationto a UE. It will be noted that an analogous organization can be adoptedfor the uplink. In the example represented, the control plane comprisesthree logical channels for the sending of call control information (CC),mobility management information (MM) and radio resources controlinformation (RR), respectively, destined for the corresponding RRCentity of the UE, and the user plane comprises two logical channels forthe sending of user information. The RRC stage 15A controls the RLCstage 16A to create an instance of RLC module 160 for each logicalchannel.

In addition to other functions, not shown, the MAC stage 17A comprises,for the dedicated channels relating to the relevant UE, a channelswitching module 170 and a transport format combination selection module171. As shown diagrammatically by the blocks 172, 173, the RRC stagecontrols the module 170 to multiplex the logical channels of the controlplane on a first dedicated transport channel TrCH 1 and the logicalchannels of the user plane on a distinct dedicated transport channelTrCH 2. By observing the bit rates on the logical channels associatedwith the transport channels, the module 171 selects the appropriatetransport format combination from among the TFCS supplied by the RRCstage 15A, and delivers the corresponding indication TFCI to layer 1.

The TFCS chosen by the RRC stage 15A can, for each combination, impose ahigher redundancy on the channel coding applied to TrCH 1 than on thatapplied to TrCH 2. For example, the turbocode can be assigned to TrCH 1while a convolutional code is assigned to TrCH 2. The differentiationmay also be achieved at the rate matching and/or CRC level.

The RRC stage 15A further controls the coding and multiplexing stage 18Aso that two physical channels (PhCH 1 and PhCH 2) are used to send thedata respectively emanating from the two dedicated TrCHs. These twoPhCHs j are linked to the radio stage 19A to which the RRC stage 15Asupplies the parameters SF_(j),i_(j) of the channel codes to be used.

By providing distinct dedicated physical channels for the signalinginformation and the user data, it is possible to increase the robustnessto noise of the signaling information while effectively managing theradio resources. The RRC sublayer can in particular allocate a higherspreading factor to PhCH 1 carrying the signaling information than toPhCH 2 carrying the user data, the latter channel having a higher symbolbit rate. By using a single PhCH, the sending of the same informationwould have required the allocation of a channel code of smallerspreading factor, i.e. closer to the root of the tree of FIG. 5, therebymobilizing more code resource (for example, it may be seen in FIG. 5that it is less effective to allocate the code c_(2,1) to a single PhCHof higher global bit rate than to allocate the codes c_(8,1) and c_(4,2)respectively to the channels PhCH 1 and PhCH 2, thereby leaving the codec_(8,2) available for another user).

If the base station is short of channel codes, it is possible to assignit a new scrambling code.

The RRC sublayer can control the enhanced robustness to noise in respectof the signaling information by adjusting the downlink target powercontrol values SIR_(target,1), SIR_(target,2). WithSIR_(target,1)>SIR_(target,2), the servo-control achieves a highertransmission power on PhCH 1 than on PhCH 2, by way of the commands TPC₁and TPC₂ returned on the uplink. Increasing the transmission power onPhCH 1 alone is better from the interference point of view thanincreasing the transmission power on a single PhCH that would carry thesame amount of information.

Alternatively, or additionally, the RRC stage 15A of UTRAN can adjustthe power levels of channels PhCH 1 and PhCH 2 directly rather thanthrough the servo-control loop using the parameter SIR_(target).

In macrodiversity mode, the radio signals are transmitted to the UE fromat least two base stations 13. Layer 1 may be regarded as apportionedbetween these base stations (or node B). The serving RNC can control theenhanced robustness to noise in respect of the signaling information bydirecting the TrCH 1, and hence PhCH 1 to the base station with whichthe radio link is of better quality and the TrCH 2/PhCH 2 to anotherbase station with which a link exists. The multiple receivers providedin the UE to support the macrodiversity mode are then used,relinquishing this mode, to receive the information along differentpropagation paths.

FIG. 7 diagrammatically shows entities of the bottom layers of a UEinvolved in accordance with an embodiment of the invention in thesending of dedicated information to UTRAN. It will be noted that ananalogous organization may be adopted for the downlink. To simplify theexample, consideration is given to the processing of a single logicalchannel of the user plane, this logical channel receiving IP datagramsfrom layer 3. The datagram flow carries control information mixed withuser data.

The RRC stage 15B controls the RLC stage 16B to create an instance ofRLC module 161 for the logical channel, and so that this module 161carries out a discrimination, at the moment of segmentation, betweenfirst data units RLC-PDU including information of a specified type (forexample control) and second data units RLC-PDU not including informationof the specified type. The module 161 analyzes the incident flow on thefly and signals the MAC sublayer as to which are the first and secondRLC-PDU units, for example by means of a flag placed in the RLC headerof each RLC-PDU unit, or by means of a parameter of a communicationprimitive between the two sublayers.

In addition to other functions, not shown, the MAC stage 17B comprises achannel switching module 175 and a transport format combinationselection module 176. As shown diagrammatically by the block 177, theRRC stage controls the module 175 to separate the logical channel of theuser plane into two distinct dedicated transport channels TrCH 1 andTrCH 2. TrCH 1 receives the first RLC-PDU units, while TrCH 2 receivesthe second RLC-PDU units. This separation is performed on the basis ofthe indications supplied by the module 161 with each RLC-PDU unit(header or primitive). By observing the bit rates on the two dedicatedtransport channels, the module 176 selects the appropriate transportformat combination from among the TFCS supplied by the RRC stage 15B,and delivers the corresponding indication TFCI to layer 1.

The TFCS chosen by the RRC stage 15B can, for each combination, impose ahigher redundancy on the channel coding applied to TrCH 1 than on thatapplied to TrCH 2. For example, the turbocode can be assigned to TrCH 1while a convolutional code is assigned to TrCH 2. The differentiationmay also be achieved at the rate matching and/or CRC level.

The RRC stage 15B further controls the coding and multiplexing stage 18Bso that the two TrCHs are multiplexed on a single physical channel. ThisPhCH is linked to the radio stage 19B to which the RRC stage 15Bsupplies the parameters SF,i of the channel code to be used.

In the example of FIG. 7, where the dedicated transport channels aregrouped onto one and the same physical channel, the differentiation ofthe immunity to noise results from the transport formats defined by theRRC sublayer and selected by the MAC sublayer. Of course, it would alsobe possible to use a process similar to what was described withreference to FIG. 6, using several PhCHs.

The analysis of the flow by the RLC sublayer comprises an examination ofone or more headers contained in the IP datagrams, making it possible toidentify the segmented data units which contain the desired information.The nature of this information may depend on the protocols used in thehigher layers, on the applications supported, on choices of the cellularnetwork operator, etc.

The discrimination can for example be based on:

the type of service field (TOS) of each IP datagram, in particular theso-called “reliability flag” thereby possibly helping to protect certainIP datagrams more than others. For a description of the IP headers, see“Internet Protocol”, Request for Comments (RFC) 791 published by theInternet Engineering Task Force (IETF), September 1981;

the type of protocol field contained in the IP header of each datagram,thereby making it possible to protect control information such as thatpertaining to the ICMP protocol (“Internet Control Message Protocol”,RFC 792, IETF, September 1981) or RSVP protocol (“Resource ReSerVationProtocol (RSVP)”, RFC 2205, IETF, September 1997) more than otherstransmitted according to protocols serving more especially for thetransport of user data, such as UDP (“User Datagram Protocol”, RFC 768,IETF, August 1980). It is thus possible to ensure that importantinformation, such as indications of expiry of time to live (TTL) or ofwrong destination address of certain datagrams, are routed under thebest conditions over the radio interface;

a transport layer protocol header such as for TCP (“Transmission ControlProtocol”, RFC 793, IETF, September 1981). It is thus possible to ensurethat important information of the transport protocol (for exampleacknowledgement or reset messages) are routed under the best conditionsover the radio interface. TCP uses relatively long timeouts (a fewseconds), so that the protection of this signaling informationappreciably improves the effectiveness of the protocol;

an application layer protocol header. This makes it possible for exampleto favor network management applications (SNMP protocol, “A SimpleNetwork Management Protocol (SNMP)”, RFC 1157, IETF, May 1990) or filetransfer applications (FTP protocol, “File Transfer Protocol (FTP)”, RFC959, IETF, October 1985) with respect to web browsing (HTTP protocol,“Hypertext Transfer Protocol”, RFC 1945, IETF, May 1996). If TCP is usedin layer 4, the indication of the application protocol may be found inthe TCP header. If UDP is used in layer 4, the indication is found inthe data part. Another example consists, within a real-time applicationsuch as telephony over IP, in favoring the control information ascompared with the coded real-time signal, i.e. the RTCP protocol ascompared with the RTP protocol (see “RTP: A Transport Protocol forReal-Time Applications”, RFC 1889, IETF, January 1996).

What is claimed is:
 1. A method of transmitting radio signals based onat least one data flow toward a radio communication station, comprisingthe steps of: processing separately, in a radio link control stage,first data units containing information of a specified type and seconddata units not containing information of the specified type; supplyingthe data units to a medium access control stage which delivers the firstdata units along a first dedicated transport channel and the second dataunits along at least one second dedicated transport channel; supplyingthe data units delivered along said dedicated transport channels to acoding and multiplexing stage (18A, 18B) to form at least one symbolstream pertaining to a dedicated physical channel; supplying each symbolstream to a radio transmission stage; and controlling the coding andmultiplexing stage and/or the radio transmission stage to providegreater protection against noise along the first dedicated transportchannel than along the second dedicated transport channel.
 2. The methodas claimed in claim 1, wherein the information of the specified type isinformation pertaining to a signaling protocol.
 3. The method as claimedin claim 1, wherein the coding and multiplexing stage is controlled toapply a channel coding exhibiting a higher redundancy in the firstdedicated transport channel than in the second dedicated transportchannel.
 4. The method as claimed in claim 1, wherein the coding andmultiplexing stage is controlled to form a first symbol stream relatingto a first dedicated physical channel based on the first dedicatedtransport channel, and at least one second symbol stream relating to asecond dedicated physical channel based on at least one second dedicatedtransport channel.
 5. The method as claimed in claim 4, wherein theradio transmission stage is so controlled that the transmitted radiosignals have a first component along the first dedicated physicalchannel and a second component along the second dedicated physicalchannel, and that the first component has a greater transmission powerthan the second component.
 6. The method as claimed in claim 4, whereinthe dedicated physical channels are multiplexed by a spread spectrumtechnique, and wherein the coding and multiplexing stage and the radiotransmission stage are so controlled that the first symbol stream has asmaller symbol bit rate than the second symbol stream, and that thefirst dedicated physical channel is associated with a higher spreadingfactor than the second dedicated physical channel.
 7. The method asclaimed in claim 4, wherein the radio signals are transmitted from atleast two base stations, the radio transmission stage being apportionedamong said base stations, and wherein the first and second symbolstreams are supplied to the radio transmission stage in distinct basestations, so as to form radio signals transmitted along differentpropagation paths.
 8. The method as claimed in claim 1, wherein theradio link control stage separately receives a first data flow belongingto a control plane, from which it forms the first data units, and atleast one second data flow belonging to a user plane, from which itforms some at least of the second data units.
 9. The method as claimedin claim 8, wherein the information of the specified type comprisesradio resource control information and/or mobility managementinformation and/or call control information.
 10. The method as claimedin claim 1, wherein the radio link control stage receives a data flowbelonging to a user plane, from which it forms the data units, whilediscriminating the first and second data units based on an analysis ofsaid flow.
 11. The method as claimed in claim 10, wherein said data flowis composed of IP datagrams.
 12. The method as claimed in claim 11,wherein the analysis of the flow comprises an examination of a type ofservice field and/or of a type of protocol field included in a header ofeach IP datagram.
 13. The method as claimed in claim 11, wherein theanalysis of the flow comprises an examination of a transport layerprotocol header and/or of an application layer protocol header includedin each IP datagram.
 14. An access network for a radio communicationsystem, comprising a radio link control stage, a medium access controlstage, a coding and multiplexing stage and a radio transmission stage,wherein the radio link control stage has means for processing separatelyfirst data units containing information of a specified type and seconddata units not containing information of the specified type, wherein themedium access control stage has means for receiving said data units andmeans for delivering the first data units along a first dedicatedtransport channel and the second data units along at least one seconddedicated transport channel, wherein the coding and multiplexing stagehas means for receiving the data units delivered along said dedicatedtransport channels and means for forming at least one symbol streampertaining to a dedicated physical channel and supplied to the radiotransmission stage, and wherein the coding and multiplexing stage and/orthe radio transmission stage are controlled to provide greaterprotection against noise along the first dedicated transport channelthan along the second dedicated transport channel.
 15. The accessnetwork as claimed in claim 14, wherein the information of the specifiedtype is information pertaining to a signaling protocol.
 16. The accessnetwork as claimed in claim 14, wherein the coding and multiplexingstage is controlled to apply a channel coding exhibiting a higherredundancy in the first dedicated transport channel than in the seconddedicated transport channel.
 17. The access network as claimed in claim14, wherein the coding and multiplexing stage is controlled to form afirst symbol stream relating to a first dedicated physical channel basedon the first dedicated transport channel, and at least one second symbolstream relating to a second dedicated physical channel based on at leastone second dedicated transport channel.
 18. The access network asclaimed in claim 17, wherein the radio transmission stage is socontrolled that the transmitted radio signals have a first componentalong the first dedicated physical channel and a second component alongthe second dedicated physical channel, and that the first component hasa greater transmission power than the second component.
 19. The accessnetwork as claimed in claim 17, wherein the dedicated physical channelsare multiplexed by a spread spectrum technique, and wherein the codingand multiplexing stage and the radio transmission stage are socontrolled that the first symbol stream has a smaller symbol bit ratethan the second symbol stream, and that the first dedicated physicalchannel is associated with a higher spreading factor than the seconddedicated physical channel.
 20. The access network as claimed in claim17, wherein the radio signals are transmitted from at least two basestations, the radio transmission stage being apportioned among said basestations, and wherein the first and second symbol streams are suppliedto the radio transmission stage in distinct base stations, so as to formradio signals transmitted along different propagation paths.
 21. Theaccess network as claimed in claim 14, wherein the radio link controlstage separately receives a first data flow belonging to a controlplane, from which it forms the first data units, and at least one seconddata flow belonging to a user plane, from which it forms some at leastof the second data units.
 22. The access network as claimed in claim 21,wherein the information of the specified type comprises radio resourcecontrol information and/or mobility management information and/or callcontrol information.
 23. The access network as claimed in claim 14,wherein the radio link control stage receives a data flow belonging to auser plane, from which it forms the data units, while discriminating thefirst and second data units based on an analysis of said flow.
 24. Theaccess network as claimed in claim 23, wherein said data flow iscomposed of IP datagrams.
 25. The access network as claimed in claim 24,wherein the analysis of the flow comprises an examination of a type ofservice field and/or of a type of protocol field included in a header ofeach IP datagram.
 26. The access network as claimed in claim 24, whereinthe analysis of the flow comprises an examination of a transport layerprotocol header and/or of an application layer protocol header includedin each IP datagram.
 27. A radio communication terminal, comprising aradio link control stage, a medium access control stage, a coding andmultiplexing stage and a radio transmission stage, wherein the radiolink control stage has means for processing separately first data unitscontaining information of a specified type and second data units notcontaining information of the specified type, wherein the medium accesscontrol stage has means for receiving said data units and means fordelivering the first data units along a first dedicated transportchannel and the second data units along at least one second dedicatedtransport channel, wherein the coding and multiplexing stage has meansfor receiving the data units delivered along said dedicated transportchannels and means for forming at least one symbol stream pertaining toa dedicated physical channel and supplied to the radio transmissionstage, and wherein the coding and multiplexing stage and/or the radiotransmission stage are controlled to provide greater protection againstnoise along the first dedicated transport channel than along the seconddedicated transport channel.
 28. The radio communication terminal asclaimed in claim 27, wherein the information of the specified type isinformation pertaining to a signaling protocol.
 29. The radiocommunication terminal as claimed in claim 27, wherein the coding andmultiplexing stage is controlled to apply a channel coding exhibiting ahigher redundancy in the first dedicated transport channel than in thesecond dedicated transport channel.
 30. The radio communication terminalas claimed in claim 27, wherein the coding and multiplexing stage iscontrolled to form a first symbol stream relating to a first dedicatedphysical channel based on the first dedicated transport channel, and atleast one second symbol stream relating to a second dedicated physicalchannel based on at least one second dedicated transport channel. 31.The radio communication terminal as claimed in claim 30, wherein theradio transmission stage is so controlled that the transmitted radiosignals have a first component along the first dedicated physicalchannel and a second component along the second dedicated physicalchannel, and that the first component has a greater transmission powerthan the second component.
 32. The radio communication terminal asclaimed in claim 30, wherein the dedicated physical channels aremultiplexed by a spread spectrum technique, and wherein the coding andmultiplexing stage and the radio transmission stage are so controlledthat the first symbol stream has a smaller symbol bit rate than thesecond symbol stream, and that the first dedicated physical channel isassociated with a higher spreading factor than the second dedicatedphysical channel.
 33. The radio communication terminal as claimed inclaim 30 wherein the radio signals are transmitted from at least twobase stations, the radio transmission stage being apportioned among saidbase stations, and wherein the first and second symbol streams aresupplied to the radio transmission stage in distinct base stations, soas to form radio signals transmitted along different propagation paths.34. The radio communication terminal as claimed in claim 27, wherein theradio link control stage separately receives a first data flow belongingto a control plane, from which it forms the first data units, and atleast one second data flow belonging to a user plane, from which itforms some at least of the second data units.
 35. The radiocommunication terminal as claimed in claim 34, wherein the informationof the specified type comprises radio resource control informationand/or mobility management information and/or call control information.36. The radio communication terminal as claimed in claim 27, wherein theradio link control stage receives a data flow belonging to a user plane,from which it forms the data units, while discriminating the first andsecond data units based on an analysis of said flow.
 37. The radiocommunication terminal as claimed in claim 36, wherein said data flow iscomposed of IP datagrams.
 38. The radio communication terminal asclaimed in claim 37, wherein the analysis of the flow comprises anexamination of a type of service field and/or of a type of protocolfield included in a header of each IP datagram.
 39. The radiocommunication terminal as claimed in claim 37, wherein the analysis ofthe flow comprises an examination of a transport layer protocol headerand/or of an application layer protocol header included in each IPdatagram.